<!--左边导航菜单-->
    <ul id="left-nav" class="nav nav-list sidenav">        
        <li ><a href="#student" class="nav-header collapsed" data-toggle="collapse"> 
            <i class="glyphicon glyphicon-th-large"></i> 学生管理
            <span class="pull-right glyphicon glyphicon-chevron-down"></span></a>
             <ul id="homework" class="nav nav-list collapse secondmenu" style="height: 0px;">
                <li ><a href="{:U('Index/index')}"><i class="glyphicon glyphicon-th-list"></i> 学生管理</a></li>
                <li ><a href="{:U('Index/showHomework')}"><i class="glyphicon glyphicon-calendar"></i> 作业浏览</a>
                </li>
                <li ><a href="{:U('Index/searchHomework')}"><i class="glyphicon glyphicon-calendar"></i> 作业查询</a>
                </li>
            </ul>
        </li>
    </ul>
